Aryl and aliphatic carboxylic acids have a variety a variety of applications in industries as anti-inflammatory drugs, fine chemicals, etc. the prior art describes the catalyst systems for employment in the processes for the preparation of carboxylic acids using the carbonization reaction on a variety of substrates. So for the most preferred catalyst system has been the homogeneous transition metal catalysts, typically palladium complexes. Generally, the various catalyst systems used for the hydrocarboxylation of olefins and comprises of a palladium source, a phosphine ligand, and a hydrogen halide promoter. Reference can made of Bittler et al. (Angew. Chem. Int. Eng. Ed., 7, 1968, 329), who described the hydrocarboxylation of olefins using a catalyst system comprising of palladium source as PdCl2 or PdCl2 (PPh3)2, a ligand as triphenylphosphine (PPh3) and HCl, has been found to occur only under drastic conditions such as 300 to 700 atm of carbon monoxide pressure. Oi et al (J. Mol. Catal. A: Chem., 115, 1997, 289) have reported hydroesterification of styrene using cationic palladium complexes which proceeds under mild reaction conditions (20) atm, 80° C.) to give 91 to 94% product yield four hours (TOF˜11 h−1) with a n:iso ratio of 60: recently Seayad et al (Ind. Eng. Chem Res., 37, 1998, 2180) have a catalyst system consisting of Pd(Oac)2, excess PPh3 and p-toluenesulphonic acid (TsOH), with a n:iso ratio of 35:65 even though various palladium phosphine complexes with N-containing ligands had not been used by then. The drawbacks for these catalyst systems lie in the law yield and reaction rates along with the drastic operating conditions. Thus it was necessary to search for a better process wherein the yield, selectivity are good using milder operating milder operating conditions.
Reference is made to U.S. Pat. No. 6,069,253 wherein Chaudhari et al have described the preparation of metal complexes containing a semilabile anionic ligand, which is a chelating organic compound containing a N-donor and a O−group. Their appropriate use as catalysts for the preparation of the saturated carboxylic acids and esters by the hydrocarboxylation of the olefinically unsaturated compounds has been described in full in U.S. Pat. No. 6,294,687 by the same authors. Describes the process describes the use of a metal complex catalyst with a N—O chelating ligand, a protonic acid and a alkali-metal halide as promoters, in presence or absence of an 120° C. for a reaction period of 30 to 180 minutes under a total pressure of 1 to 40 atmospheres, gained the system major advantages. The high turnover frequencies (˜2600 h−1) observed along with the height selectivity of >98% of the desired iso-product are some of the distinguishing features of the system. However, being a homogeneous catalyst, the system suffered from major drawback of catalyst-product separation and proper recycle, obviating the need for recyclable heterogeneous catalysts.
An important method for hydrogenising homogeneous catalysts is the application of two-phase systems comprising an aqueous phase containing water-soluble organometallic catalysts and a water immiscible phase (E. G. Kuntz, CHEMTECH, 17, 1987, 540; EP 0107006; B. Cornils, W. A. Herrmann (Eds.), Aqueous phase Organometallic Catalysis, Wiley—VCH, 1998, Weinheim) Reference can be made to recent publication (Chem. Commun. 2000, 1239; J. Mol. Catal. A; Chem, 181 (1–2), 2002, 221); where a novel water-soluble palladium complex catalyst has been proposed for the hydrocarboxylation of olefins giving high selectivity (>98%) to the iso-product. The drawback of this system however was the much lower reaction rates (TOF˜280 h−1 in comparison of the homogeneous counterpart.
Supported aqueous phase catalysis (SAPC) is another method for the heterogenization of homogeneous catalysts, wherein in water-soluble catalyst martial is contained in the thin film of water adhered to the surface of a high surface area inorganic solid support (U.S. Pat. No. 5,736,980 and U.S. Pat. No. 5,935,892). Reference is made to U.S. Patent publication No. 2002-0137964 wherein Jayasree Seayad, et al has described a process for the preparation of saturated carboxylic acid esters using a novel supported aqueous catalyst by carbonylation reaction. The drawbacks are, very low yields (˜20%) and selectivity to the desired iso-product (˜55–60%0.
Various other reports attempted the use of supported catalysts for carbonylation reactions. Reference can be made of Wu (U.S. Pat. No. 5,135,026), wherein palladium/copper catalyst support on Montmorillonite KSF, was used for carbonylation of 4-isobuylstyrene in presence of (+)-neomethyldiphenylphosphine as a ligand and Tetrahydrofuiran as solvent at 100° C., 300 psig of carbon monoxide pressure for ˜92 hours, producing good selectivity (˜97%) to the desired product. Other variations regarding the different cyclic ligands have been discussed in the same. Other relevant references are of Tanielyan et al (U.S. Pat. No. 6,025,295) wherein various supported palladium complexes have been reported to exhibit catalytic property towards carbonization reactions. The main drawbacks of most of the reports are the poor conversion, turnover frequency and selectivity. The stability of the catalysts is also a major issue in all of these cases.